1. Field of the Invention
The present invention relates to an image processing device, an image forming apparatus and an image processing method.
2. Description of Related Art
In recent years, there has been a problem in an image forming apparatus, such as a copying machine, a printer, and the like, that density unevenness (a density gradient) is generated in a main scanning direction or a sub-scanning direction in an image formed and output to a sheet. It is known that the factors for this density unevenness are the inclination of the mounting position of a laser unit, and the like, in an optical writing device; a variation in an optical path length; a distortion of a lens; a charging status of a photoconductive drum; the inclination of the mounting position thereof, and the like.
As such, according to Japanese Patent Application Laid-open Publication Nos. 2007-264371 and 2007-264364, the following technique to correct the density unevenness in an image is disclosed. That is, for example, patches having the same density are generated at a plurality of places which are respectively shifted in a direction perpendicular to a rotating direction on which an image carrier is rotated, and each density value of the generated patches is measured. Then, a corresponding relationship between the measured density and a density tone value of the patches is obtained, and the tone value input based on the obtained corresponding relation ship is converted, thereby a γ table is corrected.
However, when the density unevenness correction is performed in the image for each of the colors of C(cyan), M(magenta), Y(yellow) and K(black), the color mixture proportion of these four colors may be off-balanced. As a result, there has been a problem that the gray balance or the balance of coloration may be disturbed.